Currently, there are many kinds of sockets with various sizes. Thereby it is necessary to indicate the size of a socket. In one prior art, the socket has two annular recesses at two sides. Each recess has a protrusion. Color strips are adhered on the recess for indicating the size of the socket. The stripes are coated with oil or films as a protection layer. The stripes serve to indicate the size of the socket by two different specifications. In one prior art, the socket is formed with slide-stop trenches. A concave indication portion is formed on the periphery of the socket. Color layers are formed on the concave portion.
However all in the prior art have color layers coated on the peripheries of sockets. Protection layers or electric plating processes are used to protect the color layers. The sockets are frequently used tools. They are easy to wear or corrode in use or storage. Thereby above mentioned ways are not preferred. There is an eager demand for a novel one which can improve the prior art defects.